This invention relates to a signal control apparatus which is suitable for use in a time division multiple access communication network which is typically a mobile telephone system.
A conventional mobile telephone system comprises a base station and a plurality of mobile stations. The base station has a predetermined service area generally called a cell. The mobile stations are movable in the cell. The station can select a selected mobile one of the mobile stations for communication by the use of a radio signal.
When communication is carried out in the mobile telephone system, the radio signal is received as a received signal by the selected mobile station. In this event, it is desirable that the received signal has a received strength of predetermined value.
However, it is unavoidable that the received strength varies dependent on a distance between the base station and the selected mobile station. Namely, the received strength increases when the distance is short. When the received strength becomes extremely higher than the predetermined value, the communication is adversely affected.
In order to produce the radio signal, the base station includes a signal control apparatus already known. For example, a conventional signal control apparatus is disclosed in U.S. Pat. No. 4,592,073 issued to Kyoji Watanabe and assigned to NEC Corporation. The signal control apparatus is for controlling an apparatus input signal to produce an apparatus output signal and comprises a producing, a detecting, a comparing, and a processing circuits which will be described in the following.
The producing circuit is for producing a reference signal. The detecting circuit is for detecting the apparatus output signal to produce an output waveform signal representative of a waveform which the apparatus output signal has. The comparing circuit is for comparing the output waveform signal with the reference signal and produces a difference signal representative of a difference between the output waveform signal and the reference signal. The processing circuit is for processing the apparatus input signal into the apparatus output signal under control by the difference signal. The apparatus output signal is transmitted as the above-mentioned radio signal from the base station.
However, the conventional signal control apparatus has a disadvantage in that it is difficult to change a strength of the apparatus output signal as will be discussed in detail with reference to the drawing.